common circuit elements week 2

what is giga (G)?

10^9

what is mega (M)?

10^6

what is kilo (k)?

10³

what is milli (m)?

10^-3

what is micro (µ)?

10^-6

what is nano (n)?

10^-9

what is pico (p)?

10^-12

what is femto (f)?

10^-15

what are conductors in a common circuit?

wires

what does the combination of both voltage and current sources mean in a common circuit?

power source

what are common circuit elements?

conductors

voltage source

current source

resistors

what are the two different types of conductors (wires)?

short circuit and open circuit

what is a short circuit conductor (wire)?

two points in a circuit being connected together by an ideal conductor

• V = 0 (voltage between the ends of the ideal conductor is always zero)

• all points in a circuit are considered as a single node

what is an open circuit conductor?

no conductors or other circuit elements are connected between two parts of a circuit

• i = 0 (no current can flow through an ideal open circuit)

what are the two different types of voltage sources?

independent voltage source and dependent voltage source

what does an independent voltage source do?

provides constant voltage across its terminals

it is independent of other elements connected to it and the current flowing through it (eg batteries (dc), wall power socket (ac))

is it possible to draw an ideal circuit?

yes, but definitions of various circuits will conflict

what is wrong with this ideal circuit?

this is a closed circuit, so voltage = 0V. however, the definition requires that the voltage = 12V. we must assume we have components to absorb voltage, thus avoiding the conflict

what does a dependent/controlled voltage source do?

voltage supply depends on other components in the circuit

name the two types of dependent/controlled voltage sources:

voltage-controlled voltage source and current-controlled voltage source

what is the difference between a voltage-controlled voltage source and a current-controlled voltage source?

voltage-controlled: voltage is equal to a constant times voltage across a terminal pair elsewhere in the network

• gain parameter unit: V/V (unitless)

current-controlled: voltage is equal to a constant times current elsewhere in the circuit

• gain parameter unit: ohm (V/A)

both voltage sources are represented as a diamond-shaped symbol with an + and -

why is the voltage source diamond-shaped and not circular?

it is a dependent/controlled voltage source

what is the unit of the 3ix in this circuit?

volts, as this is a voltage source

what does an independent current source do?

forces a specified current to flow in the circuit through itself

currents through this source are independent of elements connected to it and of the voltage across it

what is important about these diagrams of an independent current source?

there are no pluses or minuses to denote direction

what does a dependent/controlled current source do?

the current flowing through the dependent current source is determined by the current or voltage elsewhere in the circuit

what is the difference between a voltage-controlled current source and a current-controlled current source?

voltage-controlled current source: current is equal to constant times voltage across a terminal pair elsewhere in the network

• gain parameter unit: A/V or 1/Ω

current-controlled current source: current is equal to constant times current elsewhere in the circuit

• gain parameter unit: A/A or limitless

state ohm’s law

voltage across an ideal resistor is proportional to its current i (v = iR)

unit: ohms (Ω)

• because it’s proportional, graph is a straight line through the origin

what is the symbol of conductance?

G

what are the two conductance formulas?

v/i = R

i/v = 1/R

G = 1/R

(conductance) = 1/(resistance)

• unit: ohm^-1 or S

i = Gv

(current) = (conductance) x (voltage)

• unit: A

what are the formulas for the power of a circuit element?

p = vi

(power) = (voltage) x (current)

• unit: W or VA

p = Ri²

(power) = (resistance) x (current)²

p = v²/R

(power) = (voltage)²/(resistance)

what does positive power denote?

energy is being absorbed by the device (load)

what does negative power denote?

energy is being supplied by the device (source)